Tanning hides and skins



No Drawing. Application filed February 11,

@Alfllllhllf ERNEST WYNDHAIVL MERRY, OF SHEFFIELD,

ENGLAND, ASfiIGNOR, BY MES'NE ASSIGN- MENTS, TD PYROTAN LEATHEROOR'PORATION, OF WILMINGTON, DELAWARE, A

CORPORATION OF DELAVIARE.

. TANNING HIDES AND SKINS.

Lei-27,221.

T 0 all whom it may concern lle it known th t l, EnNEs'r WYNDHAM lllnnnr. a subject of Great Britian, residing at Sheflield, in the countyof York, England, have invented certain new and useful improvements inTanning Hides andSkins; and I do hereby declare the following to be afull, clear, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame.

This invention relates to the tanning of hides and skins and has amongother objects the improvement of the method of tanning with a solutionof a soluble pyrophosphate and alum whereby a product of uniformly highquality is assured, and the process is maintained at a high standardefficiency.

Soluble pyrophosphates have been here-- tofore su gested as tanningagents in Letters Patent #1,039,150 and #l, l9l,527.wherein a process isdescribed for the employment of solution of pyrophosphate of sodium withalum and salt. The hides are subjected to the action of such a solutionafter the usual preliminary cleansing and unhaii'in treatment. and undercertain sneci fied conditions, to deposit aluminum pyrophosphate in theinterstices of the hide substance. The process described has attained awide commercial importance because of the high quality of the product,the

,inexpensivenessof the tanning agents and the relatively short timerequired to produce leather. The process described in said LettersPatent is particularly valuable in the production of fine'whiteleathers. Colored leathers are also produced advantageously through theoperation of the process, which in fact is universally applicable tohides and skins of every character to produce leather of a uniform anddistinctive duality.

I have discovered that the controlling factor in the production of asatisfactory product in accordance with the teaching of the LettersPatent hereinbefore referred to is the careful control of thetemperature. Relatively slight variations in the tempera ture employed,particularly an increase in the temperature beyond a well definedmaximum, results in deterioration in the quality of the product to amarked degree. The product where the temperature risesmateriilpeeification of Letters Patent.

Patented Au 29, 11922.

ally above the maximum, hereinafter specified. lacks tensile strength,and becomes more or less brittle or "grain-cracky. By carefully limitingthe temperature to a specified range, and particularly by positivelypreventing a rise in the temperature above a maximum 1 am enabled toproduce leather of a uniform character and high quality from hides andskins of Widely varying origin and texture. Success in the commercialoperation of the process of pyrophosphate tanning depends in fact uponsuch regulation of the temperature.

The range of temperature which I find to be best adapted for thepractical operation of the process lies between approximately 90 F. and107 F., the latter temperature marking the danger pointer extreme upperlimit at which deterioration of the product commences, if the materialsare permitted to attain such a temperature for any considerable period.Preferably, the range of temperature is maintained between 95 F. and 105F, the product resulting from the process, when carried out within thisrange,

being markedly superior and of uniform quality, regardless of thetexture and weight of the hides or skins which are subjected to thetanning operation.

in carrying out the process, in accordance with my invention, the hidesare preferably subjected to the usual washing, liming, unhairing, andtleshing operations. The hides are then. preferably bated and finallywashed in water or suitable cleaning solutions, until thoroughly cleanand in suitable condition for the actual tanning operations. The detailsof the preliminary treat ment may be widely varied and may follow theestablished practice of tanyards or depart therefrom in variousrespects, the preliminary treatment forming no part of my presentinvention.

The thoroughly cleaned hides are then subjected in a suitablereceptacle, for example, a pit, drum, wheel, or paddle, to the action ofthe tanning solution which includes a suitable proportion of a solublepyrophosphate, a soluble aluminum. salt and a suitable material such assodium chloride or common salt, for overcoming the astringent action ofthe aluminum salt upon the hide whereby it is maintained in porouscondition v to assimilate the active tanning agents. Preferably, sodiumpyrophosphate,

ammonia alum, and common salt are em ployed although other availablesoluble pyrophosphates may be substituted, and any soluble aluminum saltmay be advan'tageously used. For example, soda alum, potash alum,aluininum'sulphate, or aluminum chloride-may be substituted forthe-ammonia alum.

The Concentration of the solution with reference to the several'saltsmay vary somewhat depending upon the particular character of the-hidetreated; Preferably, the relative quantity of the pyrophosphat'eto thealum is maintained at the lowest ratio compatible with the successfulaccomplishment of thedesir'edobject.r Ihave discovered that.depending'upon the particular character of the hide treated, the ratioof pyrophosphate t'o thealum mayyary, from 1:4 to 1:10, the higherproportions of pyrophosphate being desirable where the hides are heavyand close in texture, and'the lower proportions being desirable in thetreatment of skins andhides joffloose texture and relativelylightweight.

Forgeneral purposes, the range of relative proportions of pyrophosphateto alum may be limited so that; the alum exceeds 5 but doesnot exceed 7times the'weight of the pyrophosphate. In calculating the relativequantities'oftherespective ingredients, I refer to thecrystallized alumcontaining 24 molecules of water of crystallization, and

substantially chemically pure anhydrous sodium 'pyrophosphate.

' The'hides are subjected in the receptacle,

as hereinbefore stated'fto a suitable quantity of the solution, thewater content: of which may vary between 20 and/l0 per cent of theveiglit of the hide substance treated.

or wheel wh-ichpermits a close regulation of. tlre temperature andinsures a thorough treatment. of the hides exposingevery portionthereofto the action of tllGSOlHtlOll. The initial temperature of, thesolution is governed by thefnecessity of. dissolving-the respectiveconstituents and is inthe neigh borhoodof flo During the tanningoperation-[the temperature tends 'to rise and,

i f the, process is not carefully watched and the tendency QQYer ned ,bysuitable control,

it will eventually rise to a point considerably above the maximumherein'before specified with attending disastrous results toth'eproduct. Iii'accordanc'e with my invention the temperature isundercontrolthroughout the operation, a suitably arranged thermometergiving a continuous indication of the term perature. hen the process iscarried out'in a wheel or drum the temperature may be reduced'atintervals when necessary by stopping rotation of the wheel or drum andopening thedoor. or closure thereof. contents of "the drum or' wheelthus remain quiescent for a period'sufficient to reduce the temperatureas deslred after whichthesprocess is continued with alternateexposure ofthe contents to reduce the temperature as may-be necessary to maintainit below the maximum of 107 F. Preferably, as hereinbefore stated thetemperature ijsfniever allowed to rise above 105 F., the best resultsbeing obtained when the range Cramps-t.

tide is between 95 F. and 105 When the tanning operation issatisfactorily concludedthe liquor iswithdrawn and the hides aresubjected'to any of the usual finishing operations. If colored leatheris to be produced the hidesmay be subjected to the action of a solutioncontaining a suitable coloring agent, preferably containing 'a tannin. I

My present invention is directed solely to the limitation of. thetemperature substantially throughout the tanning operation, whereby therise in temperature above 107FQ is positively prevented.- This Ihavefound to result in the production "of leather of uniform quality,regardless of the varia tion of other factors affecting the process.

Such factors. may be widely varied in applying the process to hides andskins of different quality andcharacter to produce commercial leather,so long as thetempera tufre'is prevented from exceeding the"maXimumhereinbefore specified substantially hroughout the tanning operation.

Various changes may therefore'be'made in the ingredients; proportions,and method of,

applying tanning agents to the hides or skins, so long as thetemperature is maintained and prevented from exceeding the range asspecified in the auneiied claims.

lclaimr" i V 1. A. method of tanning hides and skins which includesdrumming the hides in a solution containing asdluble aluminum salt and asoluble pyrop hosphate and stopping the drumming opera-tlon'atintervalswhereby th t fatui eof the mass is limited not to exceed 107F. 1 i

2. A n'ieth'od oftanning hides andskins in a quiescen icon dition whilestill in con:

tact with the. soliiti oniiiitiltlie ten'iperature is reduced, and"thereby preventing the temperature from exceeding 107 Fahrenheit.

In testimony whereof I aflix my signature.

' ERNEST WV'Y-NDI-IAMi'MERRY

